Doctor sweetening promoted by a copper salt



Dec. 20, 1955 R. H. BROWN DOCTOR SWEETENING PROMOTED BY A COPPER SALT Filed Feb. 18, 1955 vm. mm QSSmmm.

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INVENTOR.

Rasse/l H. Brown TTR/VEY nited States Patent@ DOCTOR SWEETENING PROMOTED BY A CPPER SALT Application February 18, 1955, Serial No. 489,093 17 Claims. (Cl. 196-33) This is a continuation-in-part' of my copending application Serial No. 412,706, iled February 26, 1954, now abandoned.

This invention relates to an improvement in the sweetening of sour petroleum distillates by the doctor process.

Owing tothe malodorous nature of the mercaptans present in most petroleum distillates, it is necessary to remove these compounds in order to obtain a salable material. Many methods are known for removing the mercaptan odor from mercaptan-containing distillates. These mercaptan-containing distillates are commonly known as sour distillates and the essentially mercaptanfree distillates are commonly known as sweet distillates. The more common processes in use in the petroleum industry convert the malodorous mercaptans to disuldes which are relatively innocuous with respect to odor.

The oldest and probably most common sweetening process now in use is the so-called doctor process wherein an aqueous caustic-sodium plumbite solution and free-sulfur are used to convert the mercaptans to disuliides. The doctor which arise primarily from the formation ofrinsoluble lead sulde. Frequently extremely prolonged settling times are required to remove the PbS from the hydrocarbon oil. Normally not only the doctor solution but also a black-strap layer must be-separated from the oil in order to get a PbS-free product oil. The black-strap layer which is a fairly stable emulsion of doctor solution, PbS and oil can be separated only by long settling times or by filtration. Some of the separation difliculties in the doctor process can be overcome by the use of free-sulfur in marked excess of the theoretical amount f 0.5 mol per mol of mercaptan suliur present in the oil. The amount of excess sulfur used varies with the type of stock.

An additional problem in the use of the doctor process lies in the regeneration of the spent doctor.. solution for reuse in the process. The doctor solution must be regenerated in order to provide a commercially economic` operation. Normally the spent doctor solution is regenerated by contact with free-oxygen at elevated `temperatures, e. g., 250 to 350 F. The use of lower. temperatures results in extremely long regeneration times.

A further disability of the doctor process lies in the fact-that kerosenes and heater oils that have been doctor sweetened generally show an increase in burner deposits as compared with the sour oil.

Despite these disabilities the doctor process is used because for distillates boiling in the heavier-than-gasoline range it is often the only practical way to sweeten particular sour oils.

An object of the invention is to improve the sweetening of sour hydrocarbon oils by means of the doctor process. Another object is to improve the sweetening of sour petroleum distillates which boil in the heavierthan-gasoline range, i. e., between about 325 and 650 F. Y A further object isthe sweetening `of sour hydrocarbon oils `by au improved doctor process wherein the' process has many disadvantagesk per cc. of doctor solution.

sweetening reaction and "thel regeneration reaction are carried out substantially simultaneously. A particular object is the sweetening of a sour heater oil by an improved doctorprocess wherein the substantially simultaneous regeneration of the doctor solution and the sweetening of the oil takesV place and the conventional separate spentr doctor regeneration procedure is eliminated. Other objects will become apparent in the course of the detailed description.

t is possible to eliminate the separate regeneration procedure of conventional doctor sweetening by using as the sweetening agent a doctor solution containing an effective amount of copper derived from a cupric salt and contacting the sour oil-agent mixture in the presence of at least sufficient free-sulfur to sweeten theoretically the oil and with at least sufficient free-oxygen to theoretically convert the lead suliide formed to watersoluble plumbite fora time sufcient to sweeten the oil and also to convert the lead sulfide. At the end of this time the agent phase is separated from the oil phase which is essentially sweet and the agent phase which is essentially regenerated can be recycled to the sweetening zone.

rihe hydrocarbon oil feed to the process of this invention may be any liquid hydrocarbon oil containing detectable amounts of mercaptans, i. e., oil which is sour to the conventional doctor test or which has a mercaptan number (copper number) above about l. The process is particularly suitable for the treatment of sour petroleum distillates boiling below about 700 F. Examples of these distillates are naphtha, kerosene, diesel oil, heater oil, gas oil, etc. The process may be used on distillates obtained by the fractional distillation of crude petroleum or on distillates obtained from various conversion processes such as thermal cracking, catalytic cracking, coking, etc. Sour petroleum distillates boiling in the heavier-than-gasoline range, i. e., between about 325 and 650 F., e. g;, a heater oil boiling between about 330 and 575 F. are aV preferred feed.

The sweetening agent of this invention consists of a conventional doctor solution and cupric ion derived from a cupric salt. The doctor solution is made up of an aqueous solution of an alkali metal hydroxide and the reaction product of litharge and the alkali metal hydroxide. The plumbite content is commonly given inV terms of the percent of PbO theoretically present. This content fora fresh doctor solution is usually between about 1.5 and 2.5% based on aqueous caustic solution. However, it is to be understood thatthe process is operative with any range of doctor solution compositions that are operable in a conventional doctor process.

The promoter used in the process of this invention is a copper compound, believed to contain cupric ion, which is derived from a cupric salt. It is preferred to use a cupric salt which is readily soluble in aqueous caustic solution; hereinafter thispreferred cupric salt is referred to as water-soluble'cupric salt. Examples of the watersoluble cupric salts are cupric acetate, cupric bromate, cupric bromide, cupric chlorate, cupric chloride, cupric fluoride, cupric uosilicate, cupric formate, cupric lactate, cupric nitrate, cupric sulfate, cupric methanesulfonate, cupric ethanesulfonate, cupric benzenesulfonate, and cupric toluenesulfonate. It is to be understood that these salts may be either in the hydrate form or in the anhydrous form. Because of its cheapness, it is preferred to use cupric sulfate in the form of blue vitriol, i. e., the penta-hydrate-CuSOaSHzO.

The copper, derived from the cupric salt,.is present in the doctor solution n an amount between about 0.01 and about 0.5 vgram per 100 cc. of doctor solution. More usually betweenabout 0.02 and 0.2 gram are present When operating with petroleum distillates boiling in the heavier-than-gasoline range, it is preferred to use on the order of 0.05 gram of copper per 100 cc. of doctor solution, which copper has been derived by adding about 0.2 gram of blue vitriol (CuSO4.5H2O) to the doctor solution.

In order to obtain a sweet product it is necessary to have present in the agent-sour oil contacting zone freesulfur in an amount in excess of the theoretical. The theoretical quantity of free-sulfur needed for the sweetening reaction is 0.5 mol per each mol of mercaptan sulfur present in the sour oil. For some unknown reason the use of the theoretical quantity of free-sulfur does not produce an oil that is sweet to the doctor test. The amount of excess free-sulfur necessary varies with the sour oil charged and the operating conditions. In general the higher boiling the sour oil, the more excess sulfur that is needed to produce a sweet product. Even with the most refractory feed, this process requires not more than about 175% of free-sulfur theoretically necessary to convert the mercaptans in the sour oil to disultides. (This is 75% in excess of the theoretical.) In the case of oils that are readily sweetened, it is possible to operate with an amount of free-sulfur barely in excess of the theoretical. Usually the free-sulfur usage will be between about 110% and 175 of the theoretical requirement, i. e., an excess usage of between about and 75 of the theoretical. In order to avoid the presence of corrosive sulfur and to reduce the amount of sulfur compounds present in the sweet oil, it is preferred to operate with between about 110 and 130% of the theoretical requirement of free-sulfur (between about 10 and 30% excess.)

In order to obtain the substantially simultaneous regeneration of the sweetening agent and the sweetening of the sour oil, it is necessary that free-oxygen be present in the contacting zone. The free-oxygen may be introduced in the form of a readily reducible compound such as permanganate or hydrogen peroxide, or freeoxygen itself, or in the form of atmospheric air.

Although the free-oxygen under these conditions accomplishes some mercaptan oxidation, it is primarily present to oxidize the lead sullide to the water soluble plumbite. Normally, more free-oxygen is introduced into the system than is theoretically required to convert the PbS to the plumbite. In general, the amount of free-oxygen introduced into the sweetening zone is between about 150 and 250% of the theoretical amount of free-oxygen needed to convert the lead sulfide formed in the sweetenlng reaction.

The temperature at which the sour oil-agent-oxygensulfur are contacted may be in general those temperatures used in conventional doctor treating, i. e., between about 70 and 175 F. It is to be understood that the treating temperature may be determined by the flash point of the particular sour oil charged to the process. Thus when operating with naphthas, temperatures on the order of 70 F. will be used; when operating with a kerosene, temperatures between about 100 and 120 F. may be used; and when operating with a high flash point material such as a high boiling furnace oil, temperatures as much as 150 F. or higher may be used. Still another limitation on the contacting temperature may be color formation in the oil, e. g., some kerosenes rapidly develop color bodies when exposed for prolonged times at temperatures above about 120 F. It is preferred to operate at about the maximum temperature permitted by the type of stock used in order to decrease the PbS conversion time. When operating with distillates in the heavier-than-gasoline range, particularly heater oils, it 1s preferred to operate at a temperature between about 100 and 130 F.; particularly so when using larger amounts of copper promoter. When using smaller amounts of copper promoter, temperatures as high as 150 F. are tolerable without excessive color degradation of the sweet oil. n

agent phase from the oil phase.

The contacting time is determined at the lower`temperatures by the rate of PbS conversion rather than by the rate of sweetening. At higher temperatures, these reactions proceed more or less simultaneously. The contacting must be maintained for a time at least long enough to both sweeten the oil and to convert substantially all the PbS to the plumbite. It has been found that the conversion of PbS continues after the separation of the Thus it is not necessary to carry out the conversion reaction completely in the contacting zone. Usually a completely regenerated agent will be recycled to the contacting zone when the PbS conversion reaction has proceeded to about of completion prior to separation of the agent phase from the oil phase.

The contacting time is favorably inuenced by both the temperature, the concentration of caustic in the doctor solution and by the amount of copper promoter present in the doctor solution. The higher the temperature, the shorter the contacting time needed to convert essentially all the PbS. Also, at constant caustic concentration, the higher the concentration of copper promoter derived from cupric salt in the doctor solution, the shorter the contacting time needed to convert essentially all the PbS. Thus, at 70 F. the range of contacting time is between about l and 8 hours, the longer times corresponding to the lower copper promoter content. At about 175 F. the contacting times vary from about 5 minutes to 30 minutes, the longer times corresponding to the lower copper promoter content. At about F. the contacting time varies between about 30 minutes and 4 hours; at about 130 F. the contacting time varies from about 10 minutes to about 1.5 hours. Broadly, at constant caustic concentration, the contacting time is related to contacting temperature so that the relationship of time and temperature at a temperature between about 70 and 175 F., the contacting time is between about 5 minutes and 8 hours, wherein the longer times correspond to the lower temperatures. p

The alkali metal hydroxide (caustic) concentration in the aqueous solution may be that ordinarily used in doctor sweetening, i. e., from about 5% to 20%, by weight, or more. At constant temperature and copper usage, increasing the concentration of caustic in the doctor solution has a very markedly favorable eect on the rate of regeneration of the PbS formed. At ordinary doctor sweetening temperatures, about 80 F. to 125 F., doubling the amount of caustic in the solution results in more than doubling the rate of regeneration. In order to shorten the time of sweetening-regeneration, it is desirable to operate with doctor-copper solution containing at least about 20% by weight of caustic and preferably between about 25% and about 45%, by weight, of caustic.

The annexed drawing which forms a part of this specication shows an illustrative embodiment of one particular method of utilizing the process of this invention. It is to be understood that the drawing is schematic in rature and many items of process equipment have been omitted since these may be readily added thereto by those skilled in this art.

In the drawing, sour oil from source 11 is passed by way of line 12 into heat exchanger 13. Herein the sour oil is a heater oil boiling between about 330 and 570 F. and has a mercaptan number of 65. This sour oil is derived by distillation from a high sulfur Texas crude. Herein the sour oil is substantially HzS-free and no prewash with aqueous caustic solution is carried out. When the sour oil contains appreciable amounts of HzS it is desirable to avoid loss of the caustic in the agent by prewashing the sour oil with aqueous caustic solution.

The sour oil is raised in heat exchanger 13 to a temperature high enough to provide a contacting zone temperature of about F. The hot sour oil is passed from heat exchanger 13 into line 14. A small amount of the hot sour oil is withdrawn from line 14 and is passed by way of valved line 16 into sulfur drum 17. Sulfur drum 17 is a vessel lled with elemental sulfur such as owers Vof sulfur. The hot sour oil dissolves some of this sulfur and the free-sulfur containing oil isvpassed from sulfur drum 17 into valved line 18. In this illustration, sucient free-sulfur is dissolved to have present in the sweetening zone about 25% more free-sulfur than the theoretical amount, i. e., 25 excess sulfur.

The sweetening agent from source 21 is'pa'ssed Vby way of valved line 22 into line 23. At the start of a run, only fresh sweetening agent will be present in line 23. As the run proceeds the addition of sweetening agent will be limited to makeup quantities. The amount of sweetening agent is at least enough to form a separate sweetening agent phase and may be betweenabout land 2O volume percent based on sour Avoil. In this illustration, 4 volume percent of sweetening agent i's used. The sweetening agent consists of (a) doctor solution composed of about 35% of free sodium hydroxide and about 2 g. of PbO per 100'cc. of solution, and (b) 0.2 gram `of CuSO4.5H2O per 100 cc. of doctor solution.

Air from source 26 is passedby way of line 27 into line 23. The amount of air present is enough to oxidize the PbS formed in the reaction, i. e., 2 mols of free-oxygen per molof PbS formed; about a 100% excess of air is introduced. The sweetening agent and 'the air in-line 23 are introduced by way of line 14 into reactor 428.

Reactor 28 is a vertical cylindrical vessel provided with a vent 29 and a motor-driven stirrer 31. The stirrer in this illustration is provided with three turbine blades. In order to improve agitation, reactor 28 is provided with horizontal bales 32a and 32b`.

Although a mechanically -agitated reactor is shown herein, it is to be understood that other methods of obtaining intimate contacting may be used, e. g., the reactor may be agitated with air. Also, an orifice mixer which provides a sufficient contacting time may be used.

The order of introduction of sweetening agent and freesulfur is not a critical feature vof `the invention. The free-sulfur may be added to thesour oil prior to the introduction of the sweetening agent or the free-sulfur may be added to the mixture of sour oil and sweetening agent.

However, it is preferred to mix the sweetening agent and` the sour oil before adding the free-sulfur.

The contents of reactor 28, including free-'sulfur containing oil from line 18, are maintained at a temperatureof about 130 F. for 15 lminutes in order to insure sweetening and essentially complete conversion of the PbS. Sweet oil and agent are withdrawn at a trap-out point near the upper end of reactor28 and are passed by way of line 34 into separator 36. Separator 36 is a substantially horizontal cylindrical Vessel 'providing suicient settling time for the formation of a separate agent phase, and an oil phase. Separator 36 is provided with a Vent 37 for the Withdrawal of excess air.

The lower agent phase is withdrawn from separator 36 by way of line 39. Normally the agent from line 39 Vis recycled to reactor 28 by way of 'lines 23 and.V A14. The conversion reaction results in the formation of water and sodium sulfate which dilute the agent. Periodically the agent is withdrawn from the system byway of line 39 and valved line 41.

The oil phase is withdrawn from separator 36 by way.

of line 44. This oil phase contains a very slight amount of occluded agent. The occluded agent may be removed from the sweet oil by either water washing or by coalescing. Herein the oil phase is passed from line 44 into coalescer 46. q

Coalescer 46 is a vertical cylindrical vessel vprovided with glass wool. Instead of glass .wool,4coalescer 146 may be iilled with crushed rock, Sandor rock salt., Sweethaze-free product oil is withdrawn from the topof coalescer -46 and is, passed to storage not 'shown by`- way o f.

line 4S.

The agent separated in coalescer 46 is withdrawnfrom the -.bottomp-thereof bywayof line-51. This agentmay be-r'ecycled toireactor 28 byi way of valved line 52, line 39, etc.; or it may be withdrawn from the system by way of. valved line 54.

The agent withdrawn'byrA way of lines 41 and 54 is preferablyltreatedto recover the lead content. Conventionally the lead maybe precipitated by treatment of the agent with hydrogen sulfide and oxidation of the PbS to PbO.

It is preferred to prepare the doctor-copper agent by adding a dilute aqueous solution of the copper salt to a well-stirred fresh doctor solution, i. e., one consisting of water, caustic and plumbite. Addition of the copper salt to spent doctor solution containing a large amount of phenolic compounds may result in the formation of oilsoluble copper phenolates which have an adverse eiect on the stability of the sweet oil. The buildup of phenols in the solution when sweetening oils containing appreciable amounts of phenols is tolerable under ordinary conditions; however, t is preferred vto avoid the formation of solution saturated with phenols.

It is to be understood that the embodiment described above is merely one illustration of the use of the process of this invention in the sweetening of a sour hydrocarbon oil. Y Many variations of the above will be immediately apparent to those skilled in the doctor sweetening art.

The results obtainable with the process of this invention are illustrated by the working examples below.

All the experiments described hereinafter were carried out inta three-necked glass ask having a capacity of one liter. The ask was providedwith a motor driven stirrer, a thermometer and anelectrically heated jacket. Contacting efficiency was improved by means of creases in the sides of the liask. In each run, 500 cc. ofsour oil was t charged. Except as noted, the doctor solution contained 20 weight percent of sodium hydroxide and 1.8 grams of litharge per cc. of doctorsolution. The free-sulfur was added as a one weight percent solution in xylene. Air was:bubbled through the. liquid in the ask for the regeneration'of lead sullde. The runs were carried out by adding the sour oil and the agent to the flask in thatv order. Stirring was begun immediately after adding the sour oil. Thedesired amount offree-sulfur was then added to theragitated mixture of oil andagent. Simultaneously air was b'ubbled throghthe liquid in the ask. The agitation was continued until .the stirred mixture had become clear and the agent `phase had resumed its normal clearness. Tests showed that all the leadsulde had been converted to water-soluble plumbite when the agentphase became clear'. ln all runs, the oilwas sweet to the doctor test by the time the lead sulfide had been converted.

The agent was prepared by adding cupric sulfate pentahydrate (blue vitriol) to the doctor solution. A 5% aqueous solution, of copper salt was added to a wellstirred doctor lsolution at ambient temperature- By this method a deep blue sol was easily-made with a minimum of agitation. (The agent was also prepared by adding 20% aqueous cupric sulfate to the doctor solution. However, this concentration ormed a blue gelatinous hydroxide which required considerable agitation before the gel formed was peptized to form the desired clear deep blue sol.') Apparently the copper exists in the agent in the form of colloidal cupric hydroxide formed by the reaction of ,cupric salt Aand thealkali metal hydroxide present in the doctor solution.

EXAMPLE A The inliuence of cupric promoter concentration on the time neededv to complete the conversion of lead sultde was studied in this example. In theseruns, the sour oil charged wasa kerosene having a mercaptan number of lr6, e., 16 mg.l -ofmercaptan sulfur per 100 cc. of oil and aneASTM boiling range: initial, 350 F.; 10%, 380 F;;50%, '418#Fz 90%, 461 F.; and maximum, 506 F. In each run, two volume percentof agent was present Tab-'le l C11S04.5H20, g./100 cc.-dr. soln.

Cupric ion, T'

une, gJwgoICl-dr- Minutes These data indicate that increasing the amount of cupric promoter present in the sweetening agent accelerates the rate of lead sulde conversion up to a point where further addition is ineffective.

EXAMPLE B Two runs were carried out under the same conditions as those of Example A, except that the copper agent was prepared by adding cupric chloride hydrate instead of the cupric sulfate hydrate. In one run, commercial oxygen was bubbled through the ask rather than air. In each run, 0.63 gram per 100 cc. of doctor solution of CuClz 2H2O was added to the sweetening agent. This corresponds to 0.23 gram of cupric ion per 100 cc. of doctor solution. Run 6 was carried out using air as the PbS oxidizing agent and run 7 was carried out using commercial oxygen as the oxidizing agent. In each run, the PbS conversion time was 35 minutes. These data show that cupric chloride and cupric sulfate are essentially equivalent.

EXAMPLE C T able II Time, Minutes Cupric ion, g./100 cc.-dr. soln.

Run No.

8 and 9 12 and 13 none 0. 025 0. 05

These data show clearly the difference in conversion times at lower temperatures between operation with and without the copper. Further the runs show the favorable iniluence of large amounts of cupric promotor in the agent.

EXAMPLE D The influence of temperature at constant copper concentration was studied in this example. Herein the heater oil of Example C was used as the charge. The free-sulfur usage was 5 0% in excess of the theoretical. Four volume percent of agent which had been prepared by introducing 0.2 gram per 100 cc. of doctor solution of blue vitriol, i. e., 0.05 gram of cupric ion were used. The results vof these runs are set out in Table III.

Table 111 Temge-.atum' Time, Minutes Hmm @Nano At the higher temperatures, the rates of sweetening and PbS conversion are substantially the same.

EXAMPLE E Since color of the sweet oil and color stability in storage of the sweet oil are important in commercial operations, the effect of copper concentration and temperature of contacting on these points was studied. In this example, the runs were carried out using the feed of Example C, 4 volume percent agent and 50% excess free-sulfur usage. In these runs the sweet oil was passed through ilter paper to remove traces o f occluded sweetening agent. The color of the sweet oil was taken by the Saybolt method irnmediately after ltering. The color stability of the sweet oil was determined by an accelerated method. cc. of oil were exposed to the atmospherey in an open beaker while being maintained at 200 F. for a total time of 20 hours. The color of the oil was determined and is designated hereafter as aged color. This accelerated test is known to predict with reasonable accuracy long term storage in tanks vented to the atmosphere. The results of these runs are set out in Table IV.

Table l V dr. soln.

Run No. Tempelxature,

Initial Aged EXAMPLE F In a commercial operation the doctor solution is recycled after regeneration. Therefore, for reasons of economy, it is necessary that improved solutions also be recyclable. In this example, the ability of the sweetening agent of this invention to be recycled was studied under severe conditions. The charge to the runs was a high sulfur heater oil having a mercaptan number of and an ASTM boiling range: initial, 336 F.; 10%, 330 F.; 50%, 430 F.; 90%, 506 F. and maximum, 554 F. This sour oil contains about 0.2 volume percent of phenolic compounds. The sweetening agent contained 0.05 gram per 100 grams of doctor solution of cupric promoter formed by adding blue vitriol to the doctor solution. Free-sulfur was added to the extent of a 25% excess. The temperature of contacting was 140 F. In the initial run, l0 volume percent based on charge of sweetening agent was used. The procedure involved separating the aqueous agent phase from the sweet oil phase and charging the separated agent phase to the sweetening of a fresh portion of the sour heater oil. This was continued until the sweetening agent had been utilized 7 times, that is, separate agent phase had been vcycled 6 times. The contacting time needed to convert the lead sulde was noted in each cycle and the agent pbase was analyzed for available PbO content after the nal run. The results 0f these runs are set out in Table V.

Allrunsr-werernadeat 100F. The results ofthese runs are set out 1n Table-VII below.

Agent-Puo Table VII Run No Time, Minutes t Content;

. gJlOO ce. 5 NaGH in Dr. Sweetenng- Run No.` Soln., wt. Regeneration 3 0 1. 7 percent Time, Minutes These data show that Within experimentaletror. 'the sweetening agent can be Areused at least7 times without loss of eliiciency either inthe contacting time required or the amount of available plumbite content. Thisresult is obtained without any treatment of the separated aqueous agent phase.

EXAMPLE G The effectiveness of the process was studied with respect to the sweetening of a light gas oil. This gas oil had been obtained by distillation of crude, i. e., was a virgin gas oil. The gas oil used in the agent sweetened run 29 had a mercaptan number of 10.9 and contained 2.2 mg. of hydrogen sulde per 100 cc.; the ASTM distillation was:

initial, 338 F.; 10%, 374 F.; 50%, 454 F.; 90%, 555 F. and maximum 631 F. Run 29 was carried out at 130 F. using 4 volume percent of agent containing 0.05 gram of cupric promoter and 82% excess free-sulfur. This agent had been utilized in sweetening 6 previous batches ofv sour oil. The stability of this sweet oil after 4 months storage at 90 F. in a container vented to the atmosphere was compared to a plant sweetened oil similar to the above virgin gas oil which had been sweetened by conventional doctor technique in the refinery. The results of this comparison are set out in Table VI.

Table VI Run Number 29 Run Number 30 Feed, VGO Agent, Cycle No.. Sweet Oil:

Color, Saybolt, initial Plant Blend. Plant doctor.

Color, NPA, 4 mo 1+ 2-. Acid Floc Gum, 4 mo 4.6 mg./100 m1. 5.0 ing/100 ml. Sediment, 4 ino 0.6 nig/100 1nl 0.6 lng/100 ml.

EXAMPLE H In order to determine whether or not peroxides, phenols and oleiins might precipitate in the process, a run was made under controlled conditions. Dodecane was percolated through silica gel to remove peroxides, phenols and oleiins. The dodecane was made sour by adding nbutyl mercaptan to one portion and t-octyl mercaptan to another portion. The sour dodecanes were then sweetened using copper containing doctor solution. The reaction proceeded in a manner identical with that when using petroleum distillates as the charge. Apparently, only aqueous caustic and free-oxygen are needed to effect rapid conversion of the lead sulde.

EXAMPLE I In this example, the eiect of varying the caustic concentration, at fixed copper and temperature, was determined. The feed was a kerosene having a mercaptan number of 17. The doctor-copper agent contained 0.05 g. of copper per 100 cc. of agent; 4 volume percent of agent was used and 127% of theoretical sulfur was used.

The decrease in time with increase in NaOH concentration makes it desirable 'to use caustic concentrations very much higher than those 'used in ordinary doctor sweetening. v

Thus having described the invention, what is claimed is:

l. A doctor sweetening process wherein a sour hydrocarbon oil is contacted with an agent consisting essentially of (a) doctor solution and (b) between about 0.01 and 0.5 gram, per 100 cc. of doctor solution, of copper derived from cupric salt, in an amount at least suiiicient to form separate hydrocarbon and agent phases, in the presence of at least the theoretical amount of free-sulfur needed to convert the mercaptans to disuldes, and in the presence of at least the theoretical amount of free-oxygen needed to convert essentially all the lead sulde formed, maintaining said contacting for a time at least suicient to sweeten said oil and to convert essentially all the lead sulfide formed, and separating an essentially sweet oil from an agent phase.

2. The process of claim 1 wherein said copper is obtained from a water-soluble cupric salt.

3. The process of claim 2 wherein said sulfate.

4. The process of claim 2 wherein said salt is cupric chloride.

5. The process of claim 2 wherein said salt is cupric acetate.

6. The process of claim 2 wherein said salt is cupric methanesulfonate.

7. The process of claim 2 wherein said salt is cupric benzenesulfonate.

8. The process of claim 1 wherein said agent phase is recycled to the sweetening zone.

9. The process of claim l wherein said temperature is between about F. and about 175 F. and said time is between about 5 minutes and about 8 hours, the longer times corresponding to the lower temperatures.

10. The process of claim 1 wherein said oil is a petroleum distillate boiling in the heavier-than-gasoline range.

ll. The process of claim l wherein said oil is a heavy naphtha.

12. The process of claim 1 wherein said oil is a heater oil.

13. A doctor sweetening process wherein a sour hydrocarbon oil is contacted with an agent consisting essentially of (rz) doctor solution containing at least about 20% of caustic by Weight, and (b) between about 0.02 and 0.2 gram, per cc. of said doctor solution, of copper formed by introducing a water-soluble cupric salt in said doctor solution, in an amount at least sufcient to form separate oil and agent phases, at a temperature between about 70 and 175 F. in the presence of between about and 175% of the theoretical amount of free-sulfur needed to convert the mercaptans in said oil to disullides, and in the presence of between about and 250% of the theoretical amount of free-oxygen needed to convert the lead sulfide formed in the sweetening reaction, for a time between about 5 minutes and 8 hours, the longer times corresponding to the lower temperatures, and separating an essentially sweet oil from an agent phase, which agent phase is suitable for recycle to the sweetening zone.

14. The process of claim 13 wherein said temperature is between about 100 and 130 F. and said time is besalt is cupric tween about minutes and 4 hours, the longer times corresponding to the lower temperatures.y

15. A doctor sweetening process wherein a sour petroleum distillate boiling in the heavier-than-gasoline range is contacted with an agent consisting essentially of (a) doctor solution containing between about and caustic by weight and (b) about 0.05 gram, per` cc. of doctor solution, of copper promoter derived by introducing a water-soluble cupric salt in said doctor solution, in an amount at least sufficient to form separate distillate and agent phases, in the presence of between about and 130% of the theoretical amount of freesulfur needed to sweeten said distillate and in the presence of between about and 250% of the theoretical amount of free-oxygen needed to convert the lead sulfide formed in the sweetening reaction, at a temperature between about 100 F. and 130 F. for a time between about 16. The process of claim 15 wherein said salt is cupric sulfate.

Y 17. The process of claim 15 wherein said distillate is heater oil.

^ References Cited in the file of this patent UNITED STATES PATENTS 1,789,335 Fischer et al. Jan. 20, 1931 2,591,946 Krause et al. Apr. 8, 1952 OTHER REFERENCES 'Kalishevsky et al.: Chemical Refining of Petroleum, page 205 (1942). 

1. A DOCTOR SWEETING PROCESS WHEREIN A SOUR HYDROCARBON OIL IS CONTACED WITH AN AGENT CONSISTING ESSENTIALLY OF (A) DOCTOR SOLUTION AND (B) BETWEEN ABOUT 0.01 AND 0.05 GRAM, PER 100 CC. OF DOCTOR SOLUTION, OF COPPER DERIVED FROM CUPRIC SALT, IN AN AMOUNT AT LEAST SUFFICIENT TO FORM SEPARATE HYDROCARBON AND AGENT PHASES, IN THE PRESENCE OF AT LEAST THE THEORETICAL AMOUNT OF FREE-SULPHUR NEEDED TO CONVERT THE MERCAPTANTS TO DISULFIDES, AND IN THE PRESENCE OF AT LEAST THE THEORETICAL AMOUNT OF FREE-OXYGEN NEEDED TO CONVERT ESSENTIALLY ALL THE LEAD SULFIDE FORMED, MAINTAINING SAID CONTACTING FOR A TIME AT LEAST SUFFICIENT TO SWEETEN SAID OIL AND TO CONVERT ESSENTIALLY ALL THE LEAD 